Tube coupling



FIG. 1 is a top elevational view of a tube coupling embodying the ornamental design constituting my invention;

FIG. 2 is a side view of the tube coupling shown in FIG. 1;

FIG. 3 is a bottom view of the tube coupling shown in FIG. 2;

FIG. 4 is a side elevational view of FIG. 3;

FIG. 5 is a left end view thereof; and,

FIG. 6 is a right end view thereof. 

The ornamental design for a tube coupling, as shown and described. 